1. Field of the Invention
The present invention relates to a method of and an apparatus for supplying photosensitive lithographic printing plates to an exposure device which exposes the photosensitive lithographic printing plates.
2. Background Information
For photosensitive lithographic printing plates (hereinafter, "printing plates") used in an offset rotary press for newspapers, there is a direct reproduction recording system using an OPC (organic photo conductor) photosensitive material. The OPC photosensitive material is formed by an organic photo-semiconductor being applied to a conductive supporting body such as aluminum or the like, so as to form a photoconductive photosensitive layer. In this type of a direct plate manufacturing system, the photosensitive layer is charged before exposure. As a result, after exposure, when the photosensitive layer contacts a conductive member, such as metal or the like, the electrostatic image formed by exposure is disturbed. Therefore, great care must be taken in handling the OPC photosensitive material.
Generally, a plurality of printing plates are stored or transported in a state in which they are stacked on a holding stand. When the printing plates are supplied to an exposure device, they are loaded together with the holding stand onto a supplying device which is provided adjacent to the exposure device. The printing plates stacked on the holding stand are supplied by the supplying device to the exposure device successively from the topmost plate.
A surface plate is provided in the exposure device. The printing plate is placed on the surface plate such that the photosensitive surface of the printing plate faces upward. The printing plate positioned on the surface plate is electrostatically charged, and is exposed by a laser beam or the like which is modulated in accordance with an original image. An electrostatic latent image is thereby formed. The printing plate on which the electrostatic image has been formed is removed from the surface plate and is conveyed into a developing portion.
In order to load the printing plate by the supplying device on the surface plate such that the photosensitive surface of the printing plate faces upward, the printing plates have been set in advance on the holding stand with their photosensitive surfaces facing upward. These printing plates are usually transported from the holding stand to the exposure station one by one with the upper surface thereof being sucked by suction cups or by nip rollers. Examples are illustrated in Japanese Patent Unexamined Publication No. 2-23861 and Japanese Patent Unexamined Publication No. 2-19952.
However, when the printing plates, especially the OPC photosensitive materials, are sucked by the suction cups or contact the rollers, traces of the suction cups or rollers remain on the printing plates even after exposure. A drawbacks arises in that this effects the image formed on the photosensitive surface of the printing plate.